This invention relates to the clarification of fluids containing suspended settleable solids.
Domestic sewage and other forms of waste water often contain impurities in the form of suspended solids. Examples of waste water other than sewage include drainage water containing clay or silt, clean-up and process water from food processing industries, water containing precipitated particles of heavy metals from the electroplating industry, pickle liquor from steel plant operations, waste water from the metal finishing industry, waste water from painting operations, etc. It is desirable to remove the suspended solids prior to returning the waste water to the environment. Water supplies frequently contain silt, clay, and objectionable dissolved solids which can be chemically treated to precipitate the unwanted materials. It is necessary in most instances to remove these suspensions of silt and precipitates in order to obtain water suitable for domestic and other uses. Additionally, certain liquid products containing suspended solids must be clarified to enhance their value. Conventionally, this is accomplished by passing the fluid to a clarifier where the suspended solids are permitted to settle, forming a sludge which is disposed of by suitable means. Clarified effluent is withdrawn from the top of the clarifier for use or return to the environment. Settled waste solids are suitably disposed of, e.g., in land fill.
Christopher et al in an article entitled "New Waste Water Process Cuts Plant Costs 60%", Civil Engineering--ASCE, May 1983, pages 39-41 describes an intrachannel clarifier for use in a circulating acvitated sludge sewage treatment system. According to the clarifier system described in this article, raw sewage enters the aeration basin, is aerated, then passed beneath an intrachannel clarifier wherein a portion of mixed liquor, i.e., a mixture of waste water and activated sludge, rises into the clarifier through openings in the clarifier bottom panels. As the mixed liquor flows up into the quiescent clarifier zone, solids are separated, fall down through the openings and return to the continuously flowing mixture below. Clarified effluent is removed from the quiescent zone in the upper portion of the clarifier through orifice pipes submerged about one foot beneath the water's surface. The aeration basin in which the clarifier is used is an oxidation ditch which includes a closed flow path, i.e., one or more pumps are provided for circulating the liquid through the flow path beneath the clarifier. The liquid enters beneath the clarifier at a higher pressure than the liquid exiting beneath the clarifier and at the other end of the flow path because of head loss experienced during the flow of the liquid under the clarifier.